1. Field of Invention
The present invention relates to an electric hand control especially for electrically adjustable hospital and care beds.
2. The Prior Art
Such hand controls are made of two plastic shells which combined constitute a closed housing. The assembly can be made with screws, by gluing or to ultrasound welding. Before the shells are joined, a printed circuit with switches and with a cable soldered onto it lead through a spout in the back of the hand control is inserted. In the upper plastic shell are keys, typically in the form of springy tongues, and a foil with graphics, localizing the keys and their function is mounted over the top side. By hospital and care beds it is demanded that the hand controls are humidity- and watertight, as they are washed and disinfected with the bed in washing tunnels designed especially for that purpose. In that respect it is rather difficult to make the joining of the two plastic shells properly watertight.
The object of the invention is to provide a hand control with a simplified structure, which allows for better sealing.
This is achieved according to the invention by constructing the hand control as just one shell, which means that the manufacturing of two parts and the joining of these during the assembly process is avoided, and a joining with the risk that it is not tight is avoided. The assembling is simply done by placing the parts in the shell and finally closing it with the cover foil.
By mounting the cover foil on a thread of a step down in the upper edge of the side wall of the shell, the edge of the cover foil is protected from unintended damage and at the same time the fastening is made easier as the edge in the step contributes to a unique and steady positioning of the cover foil. When the foil is mounted with an adhesive, a small surplus can be used, which collects in the crossing between the foil and the edge in the step or at least make sure that the adhesive reaches the edge. As already mentioned the hand control needs cleaning from time to time, for which purpose a distance of the side wall of the shell, preferably in one end of the hand control is lead on a level with the top side of the cover foil. This prevents accumulations of water on the top side of the hand control, just like dirt effectively can be wiped off through the opening. It is noted that the opening also contributes to an easier mounting of the cover foil.
The printed circuit and the plate with the keys can be fastened in various manners in the housing, but expediently the printed circuit is placed loosely on some support ribs while the plate is held in the housing with inter active snap lock connections. The use of screws, and particularly screws on the top side of the plate which can fret a hole in the cover foil, is thereby avoided. Altogether an even and smooth surface with a minimum of interruption is achieved, which ensures a good and lasting attachment of the cover foil.
A number of advantages are gained by constructing the plate with the keys made from a two component plastic material. So that the plate in a single process can be moulded with corresponding bricks, which constitutes the keys in a hard plastics, where the keys, preferably with strings, are connected to the surrounding part of the plate with a flexible plastic material. In embodiments of the hand control with locking function, i.e. where the switches with turn buttons are made inactive, the turn bottoms are sealed with the same two component plastic material by making the edge of the openings in the plate, wherein the turn buttons are placed, from the flexible plastic material, so that it forms a sealing against the turning knob. The two component material can also be used when securing the printed circuit and plate by equipping the plate with legs, which rests on the top side of the printed circuit with a foot for holding this. The foot is also made from the elastic plastic material, which for one thing has the advantage that the manufacturing tolerances are absorbed in the elastic feet and for another that the elasticity in the feet causes the previous mentioned snap lock connection to be held in secure mesh by the spring force. Finally it is advantageous to use a transparent plastic material for the plate when the hand control is equipped with background lighting. Thus light diodes can be mounted on the printed circuit and the light is distributed through the transparent plate and through selected completely or partially transparent areas of the cover foil, typically as markings for the keys.
Where cable connected hand controls are concerned, the cable is led through a hole in the housing, which provides basis for a good sealing. By making the hole in the housing with an oval cross section it will make the lead-in of the cable with plug easier and at the same time wider plugs can be used. Cuts in the top side of the side wall which can disturb the fastening of the cover foil and which can be difficult to seal is thereby avoided. The hole in the housing can be tube shaped, which is a good sealing surface and the spout on the cable can be equipped with sealing rings. As strain relief the spout can be equipped with a collar by the outer end, which when led into the housing rests against the inner side of the side wall of the housing. Logistically and in respect to the assembly it is an advantage to secure the cable to the printed circuit with a socket. Juggling with an unmanageable part like a printed circuit with a long cable soldered onto it in the assembly process is avoided. Logistically it is easy to make an individually adjustment of the cable length.
Further features of the invention will be explained more fully below in connection with an embodiment of the invention with reference to the accompanying drawings.